Signal-on electrochemical aptasensors with different target-induced conformations for prostate specific antigen detection

In silico maturation of DNA aptamer against the prostate-specific antigen (PSA) and kinetic analysis

The detection of the prostate-specific antigen (PSA) serves as a critical marker for the diagnosis and follow-up of prostate cancer. DNA aptamers targeting PSA have been successfully screened using the systematic evolution of ligands by exponential enrichment (SELEX) technique, complemented by in silico maturation processes. In this study, we aim to optimize a truncated aptamer, denoted as TA87, through computational methods and to analyze potential aptamer candidates in the aptamer-PSA interactions. The PSA antibody, aptamer ΔPSap4#5, and an identified but unpublished aptamer, PSAG221, were evaluated in quartz crystal microbalance (QCM) experiments alongside aptamers derived from TA87. The Tanimoto similarity score and the ZDOCK program, coupled with the ZRANK scoring function, were adopted to assess the secondary structure of single-point mutants of TA87 and their binding interactions with PSA, respectively. Detailed analyses of the aptamer-protein complexes were conducted using molecular dynamics (MD) simulations. Mutations TA87M24 and TA87M49, along with PSAG221 and TA87, showed superior ZDOCK scores compared to ΔPSap4#5. MD simulations further suggested that PSAG221 aptamer might offer enhanced binding to PSA over ΔPSap4#5. The affinity constant (KD) values for the antibody, ΔPSap4#5, PSAG221, TA87, TA87M24, and TA87M49 with PSA were determined through QCM measurements to be 0.35, 0.33, 0.35, 0.56, 0.45, and 0.51 μM-1, respectively. The experimental results showed that the truncated aptamers, TA87, and the two mutations, TA87M24 and TA87M49, did not demonstrate superior PSA binding affinity. Aptamer PSAG221 demonstrated performance comparable to that of the antibody, although slightly inferior to ΔPSap4#5. The aptamer PSAG221 reported in this study could be an alternative probe for developing future PSA aptasensor platforms.

Sandwich-Type Electrochemical Aptasensor with Supramolecular Architecture for Prostate-Specific Antigen

A novel sandwich-type electrochemical aptasensor based on supramolecularly immobilized affinity bioreceptor was prepared via host-guest interactions. This method utilizes an adamantane-modified, target-responsive hairpin DNA aptamer as a capture molecular receptor, along with a perthiolated β-cyclodextrin (CD) covalently attached to a gold-modified electrode surface as the transduction element. The proposed sensing strategy employed an enzyme-modified aptamer as the signalling element to develop a sandwich-type aptasensor for detecting prostate-specific antigen (PSA). To achieve this, screen-printed carbon electrodes (SPCEs) with electrodeposited reduced graphene oxide (RGO) and gold nanoferns (AuNFs) were modified with the CD derivative to subsequently anchor the adamantane-modified anti-PSA aptamer via supramolecular associations. The sensing mechanism involves the affinity recognition of PSA molecules on the aptamer-enriched electrode surface, followed by the binding of an anti-PSA aptamer-horseradish peroxidase complex as a labelling element. This sandwich-type arrangement produces an analytical signal upon the addition of H2O2 and hydroquinone as enzyme substrates. The aptasensor successfully detected the biomarker within a concentration range of 0.5 ng/mL to 50 ng/mL, exhibiting high selectivity and a detection limit of 0.11 ng/mL in PBS.

Structure-Switching Electrochemical Aptasensor for Rapid, Reagentless, and Single-Step Nanomolar Detection of C-Reactive Protein

C-reactive protein (CRP) is an acute-phase reactant and sensitive indicator for sepsis and other life-threatening pathologies, including systemic inflammatory response syndrome. Currently, clinical turn-around times for established CRP detection methods take between 30 min to hours or even days from centralized laboratories. Here, we report the development of an electrochemical biosensor using redox probe-tagged DNA aptamers, functionalized onto inexpensive, commercially available screen-printed electrodes. Binding-induced conformational switching of the CRP-targeting aptamer induces a specific and selective signal-ON event, which enables single-step and reagentless detection of CRP in as little as 1 min. The aptasensor limit of detection spans approximately 20-60 nM in 50% human serum with dynamic response windows spanning 1-200 or 1-500 nM (R = 0.97/R = 0.98 respectively). The sensor is stable for at least 1 week and can be reused numerous times, as judged from repeated real-time dosing and dose-response assays. By decoupling binding events from the signal induction mechanism, structure-switching electrochemical aptamer-based sensors provide considerable advantages over their adsorption-based counterparts. Our work expands on the retinue of such sensors reported in the literature and is the first instance of structure-switching electrochemical aptamer-based sensors (SS-EABs) for reagentless, voltammetric CRP detection. We hope this study inspires further investigations into the suitability of SS-EABs for diagnostics, which will aid translational R&D toward fully realized devices aimed at point-of-care applications or for broader use by the public.

Aptamer-Based Switching System for Communication of Non-Interacting Proteins

Biological macromolecules, such as DNA, RNA, and proteins in living organisms, form an intricate network that plays a key role in many biological processes. Many attempts have been made to build new networks by connecting non-communicable proteins with network mediators, especially using antibodies. In this study, we devised an aptamer-based switching system that enables communication between non-interacting proteins. As a proof of concept, two proteins, Cas13a and T7 RNA polymerase (T7 RNAP), were rationally connected using an aptamer that specifically binds to T7 RNAP. The proposed switching system can be modulated in both signal-on and signal-off manners and its responsiveness to the target activator can be controlled by adjusting the reaction time. This study paves the way for the expansion of biological networks by mediating interactions between proteins using aptamers.

Portable and Rapid Dual-Biomarker Detection Using Solution-Gated Graphene Field Transistors in the Accurate Diagnosis of Prostate Cancer

Prostate-specific antigen (PSA) is the common serum-relevant biomarker for early prostate cancer (PCa) detection in clinical diagnosis. However, it is difficult to accurately diagnose PCa in the early stage due to the low specificity of PSA. Herein, a new solution-gated graphene field transistor (SGGT) biosensor with dual-gate for dual-biomarker detection is designed. The sensing mechanism is that the designed aptamers immobilized on the surface of the gate electrodes can capture PSA and sarcosine (SAR) biomolecules and induce the capacitance changes of the electric double layers of SGGT. The limit of detections of PSA and SAR biomarkers can reach 0.01 fg mL-1 , which is three-to-four orders of magnitude lower than previously reported assays. The detection time of PSA and SAR is ≈4.5 and ≈13 min, which is significantly faster than the detection time (1-2 h) of conventional methods. The clinical serum samples testing demonstrates that the biosensor can distinguish the PCa patients from the control group and the diagnosis accuracy can reach 100%. The SGGT biosensor can be integrated into the portable platform and the diagnostic results can directly display on the smartphone/Pad. Therefore, the integrated portable platform of the biosensor can distinguish cancer types through the dual-biomarker detection.

Recent advances in the selection of cancer-specific aptamers for the development of biosensors

An early diagnosis has the potential to greatly decrease cancer mortality. For that purpose, specific cancer biomarkers have been molecularly targeted by aptamer sequences to enable an accurate and rapid detection. Aptamer-based biosensors for cancer diagnostics are a promising alternative to those using antibodies, due to their high affinity and specificity to the target molecules and advantageous production. Synthetic nucleic acid aptamers are generated by in vitro Systematic Evolution of Ligands by Exponential enrichment (SELEX) methodologies that have been improved over the years to enhance the efficacy and to shorten the selection process. Aptamers have been successfully applied in electrochemical, optical, photoelectrochemical and piezoelectrical-based detection strategies. These aptasensors comprise a sensitive, accurate and inexpensive option for cancer detection being used as point-of-care devices. This review highlights the recent advances in cancer biomarkers, achievements and optimizations made in aptamer selection, as well as the different aptasensors developed for the detection of several cancer biomarkers.

A ratiometric fluorescence sensor for 5-hydroxymethylfurfural detection based on strand displacement reaction

Since 5-hydroxymethylfurfural (HMF) becomes a neo-forming contaminant with latent harm to human health, development of new method for highly sensitive detection of HMF is extremely desirable. Herein, a novel ratiometric fluorescence sensor based on strand displacement reaction and magnetic separation was designed for sensitive and selective detection of HMF with the help of MnO₂ nanosheets. The aldehyde-functionalized DNA (S0-CHO) and HMF competed for binding to amino-functionalized magnetic beads (NH₂-MBs). Then, S0-CHO was collected from supernatant by magnetic separation. In the presence of HMF, the obtained S0-CHO induced the formation of T-shaped DNA by strand displacement reaction (SDR), lighting the fluorescence of FAM. In the absence of HMF, no S0-CHO was present to ignite T-shaped DNA. In this situation, fluorescence of Cy5 was turned on. Thus, a ratiometric fluorescence sensor for high-sensitive detection of HMF was developed. The sensor has a wide linear range from 5 nM to 5 μM. It also exhibited high selectivity against other potential interfering substances. It has been successfully applied to analyze HMF in food samples. The method has potential to be expanded to detect other molecules containing aldehyde groups and further be applied in food safety, environment and other fields.

Recent advances in nanomaterials for prostate cancer detection and diagnosis

Despite the significant progress in the discovery of biomarkers and the exploitation of technologies for prostate cancer (PCa) detection and diagnosis, the initial screening of these PCa-related biomarkers using current...

Biosensing strategies for diagnosis of prostate specific antigen

Almost from the time of its discovery, the prostate specific antigen (PSA) has been one of the most accurate and most extensively studied indicators of prostate cancer (PC). Because of advancements in biosensing systems and technology, PSA analysis methods have been substantially updated and enhanced as compared to their first instances. With the development of techniques in biosensor technology, the number of PSA biosensors that can be used in the biomedical sector is increasing year by year. Many different recognition elements and transducers have been used in the development of biosensor systems that exhibit high sensitivity, selectivity, and specificity. Here in this review, we provide a current overview of the different approaches to PSA detection.

A photoelectrochemical biosensor based on methylene blue sensitized Bi5O7I for sensitive detection of PSA

Herein, bismuth oxyiodide (Bi₅O₇I) was used as a signal probe to construct an effective sensitization structure with methylene blue (MB), combined with protein conversion strategy, and a photoelectrochemical (PEC) biosensor was constructed for sensitive detection of prostate-specific antigen (PSA). The designed biosensor had a high sensitivity and a low detection limit (LOD) of 0.047 fg mL^-1, which opened up a simple way for the detection of PSA and showed a good application prospect in clinical and medical fields.

Proximity binding induced nucleic acid cascade amplification strategy for ultrasensitive homogeneous detection of PSA

In this work, based on the powerful cycle amplification cascades of proximity hybridization-induced hybridization chain reaction and catalyzed hairpin assembly, we engineered a nonenzymatic and ultrasensitive method which combined the Mg²⁺-DNAzyme recycling signal amplification for the analysis of the human prostate specific antigen. Herein, we adopted PSA-conjugates as triggers in the self-assembly process of two hairpin DNAs (H1, H2) into the products of the CHA which could activate the HCR to induce repeated hybridization. And both ends of each adjacent sequence of the HCR products could form a unit of Mg²⁺-DNAzyme which in presence of cofactor Mg²⁺ could recognize and cyclically cleave the hairpin probes in the solution and thus generate observably enhanced fluorescent signal. Benefit from the nucleic acid circuit amplification strategy, PSA of concentration low to 0.73 pg mL^-1 was detected in this system. This homogeneous sensing method in solution avoid the use of the sophisticated equipment and complex operation, as well as addition of artificial enzyme, thus greatly reducing the constraints and complexity of experimental conditions. Moreover, considering most protein biomarkers in serum don't have their corresponding aptamers, this sensing method provide a general sensing approach for homogeneous sensitive detection of these important protein biomarkers which transfer rough antigen-antibody interactivity to smart signal amplification sensing strategies, thus exhibiting a remarkable prospect in clinical application.